In a scroll compressor the trapped volumes are in the shape of lunettes and are defined between wraps or elements of fixed and an orbiting scroll and the scroll end plates. The lunettes are generally crescent in form with the lunettes extending about 360.degree. about the assembly with the two ends thereof defining points of contact between the coacting wraps. As the orbiting scroll moves through its orbital path of motion, the points of contact between the wraps move continuously toward the center of the assembly to reduce the volume of the lunettes and thus compress the fluid trapped therein. The pressure of the fluid continues to increase until it reaches a centrally located compressor discharge. A varying pressure gradient is thus felt across the scroll which tends to both axially and radially displace the scroll as it moves through an orbital path of motion.
Eccentric bushings, swing link connectors, slide blocks and the like have all been used to insure radial compliance of the orbiting scroll. These approaches all utilize the centrifugal forces produced by the orbiting scroll to hold the scroll wraps in sealing contact during the compression process. A number of approaches have also been used to counter the axial forces acting upon the orbiting scroll. The pressure of a fluid being compressed as well as that from an external source have been used to provide a biasing pressure against the back of the orbiting scroll. U.S. Pat. Nos. 3,600,114; 3,294,977 and 3,994,633 show examples of some of these back pressure devices.
In some compressors, a back pressure chamber is located immediately behind the back plate of the orbiting scroll and is provided with a perimeter seal that traps a high pressure fluid within the sealed region. Springs are sometimes placed against the seals to mechanically bias them in sealing contact. The springs, however, will weaken with usage and localized leaks can develop thus destroying the integrity of the back pressure chamber. The spring also places an additional torque on the system which must be overcome by the compressor motor.